The present invention is directed to signal amplifiers used with a sensor such as a read head in an information storage device, and especially to such signal amplifiers having reduced input impedance.
There are many important goals in designing and operating an amplifier for use with a sensor. One such goal is low band pass corner frequency. Sensors such as magneto-resistive sensing elements require a direct current (DC) bias applied across them to operate correctly. The presence of such a DC bias may cause problems if the DC signal is passed on to amplifying elements. A low band pass corner frequency permits sensing of lower frequency signals while still rejecting DC signals and therefore contributes to a truer sensing of signals indicated by the sensor.
Needs for greater magnetic storage density in industry have been answered by various innovations. One such innovation has been perpendicular magnetic recording in which the magnetic recording medium is magnetized perpendicularly to the film plane of the medium rather than in the plane of the medium. This new technology has occasioned new design challenges. One such challenge has been that when using perpendicular magnetic recording, low corner frequency fLF is preferably about one-tenth the value of low corner frequency fLF values required for longitudinal recording applications where the magnetic recording medium is magnetized substantially in the film plane of the medium.
Prior art signal amplifiers, especially signal amplifiers for use with a read head in an information storage device, have heretofore been difficult to produce economically with low band pass corner frequency fLF.
There is a need for a signal amplifier apparatus that accommodates economic design for low band pass corner frequency.